1. Field
One or more embodiments of the present invention relate to an auto-focus method, medium, and apparatus for image-capturing, and, more particularly, to an auto-focus method, medium, and apparatus for image-capturing where the focus can be automatically adjusted at high speed without needing to switch between a normal mode and a macro mode regardless of the distance between a lens and an object by using the blur levels of a number of images.
2. Description of the Related Art
Auto-focus, a feature of modern cameras, is a technique of automatically adjusting the focus by detecting a subject based on a signal of the subject captured by a camera lens, and automatically driving a focus lens according to the result of the detection.
Efforts have been made to improve the quality of images captured by image-capturing apparatuses such as digital cameras or digital camcorders using an auto-focus function.
FIG. 1 illustrates a graph of the relationship between the precision of the focus and the position of a focus lens. The position of a focus lens of an image-capturing apparatus varies according to the distance between the focus lens and a subject. Conventionally, methods such as high pass filtering and hill climbing have been widely used where an optimum focal point is determined by comparing the precision of the focus at one focus lens position with the precision of focus at another focus lens position while continuously varying the position of a focus lens. These methods, however, require a considerable number of images to determine an optimum focal point and may thus cause a shutter lag. As such, these methods may not be suitable for use in high-speed photography.
Other conventional auto-focus methods involve obtaining images by placing a focus lens at two fixed positions, respectively; adding up the images or subtracting the images from each other in units of pixels; and determining an optimum position of a focus lens by analyzing frequency components of the results of the addition or the subtraction. However, these auto-focus methods require the edges of two images to be added or subtracted from each other to precisely coincide with each other, and also require a considerable amount of computation.
In addition, these other auto-focus methods require switching between a macro mode for performing close-range photography and a normal mode for performing regular photography. Therefore, no auto-focus methods without the requirement of mode switching have yet been suggested.